The invention relates to a fused switch unit having two connecting contacts into which a fuse holder can be inserted in order to hold a fuse link with a head contact and a foot contact, in which case a first connecting contact can be connected via a controllable interruption contact, which has a bridging element, to the foot contact or to the head contact of the fuse link. The fuse holder or the fused switch unit in this case has a fuse state indicating device for checking the fuse link which can be inserted into the fuse holder, or for checking the switching state.
Fused switch units with a fuse holder for a fuse link are known in many different embodiments both for electrical protection in buildings and dwellings and for electrical protection of machines and production plant.
In order to monitor the state of the fuse link, or the switching state, it is advantageous to provide a fuse state indicating device for fused switch units such as these. Such state indicating devices produce a generally visual signal at least whenever the contact via the fuse link can no longer be produced when the fused switch unit is in a ready to operate state, since, for example, the conductive bridge in a fusible link has blown. The state indicating device should never emit a signal when the fused switch unit is in a ready to operate state and there are no defects in the fuse link.
Depending on the contact, it is possible to provide for the fuse state indicating device also to produce a signal when the fuse holder together with the fuse link is in a ready to operate position, but the fused switch unit is in a disconnected position, in which, for example, the contact is interrupted by a switch at a point within the fused switch unit.
Fused switch units and fuse holders are known with different types of contact for such a fuse state indicating device. For example, it is possible to fit a conductor for making contact with the state indicating device, together with the fusible conductor, in the fuse link itself. However, in particular, this has the disadvantage that it complicates the production and the matching of the fuse link, since the conductor for making contact with the fuse state indicating device occupies space which is normally intended for the quartz sand used for insulation of the fusible conductor. Furthermore, during operation, the fusible conductor produces heat, which can damage the conductor for making contact with the state indicating device.
A fuse holder with an integrated connecting line for a state indicating device is known from DE 198 00 779 A1. In this case, connecting lines which connect the fuse state indicating device directly to the head contact and the foot contact of the fuse link are provided in the fuse holder. In this refinement as well, there is a risk of the connecting lines, which are located in the vicinity of the foot contact in particular, being damaged if any switching arcs occur during switching processes. In addition, both the fuse state indicating device and all the connecting lines are located inside the fuse holder, so that this provides only a small amount of flexibility for the arrangement, in particular, of the visual indication of the fuse state indicating device.
One object of the present invention is to provide a fused switch unit with a fuse holder for holding a fuse link, which has a fuse state indicating device, and with a high degree of flexibility being provided for the arrangement of the elements of the fuse state indicating device and of the corresponding connecting lines, while at the same time ensuring a high level of operational reliability and safety, and little wear.
The object is achieved by a fused switch unit according to the invention. Claims 11 to 13 relate to a fused switch system which has at least two fused switch units according to the invention, as claimed in one of claims 1 to 10.
According to the invention, the object is achieved in that a first contact of the fuse state indicating device is connected via an electrically conductive connection and exclusively to the bridging element of the interruption contact of the fused switch unit, and a second contact of the fuse state indicating device is connected directly via an electrically conductive connection to the second connecting contact of the fused switch unit.
In this case, the first contact is preferably connected via a conductor to a physically fixed end of a spring apparatus, which preloads the bridging element, of the interruption contact, with the spring apparatus also being composed of conductive material.
This firstly allows a high degree of variability to be achieved in the arrangement of the fuse state indicating device and of the corresponding connecting lines, since all the elements can be provided both in the fuse holder and in the fused switch unit. In particular, the preferred visual indication of the fuse state indicating device can be positioned, depending on the configuration of the fused switch unit, such that it is easily visible from the outside, without increasing the structural complexity.
The connecting lines for the fuse state indicating device may be located at a distance from those areas in which heat is produced during operation or in which switching arcs can occur during switching processes.
It is furthermore also advantageous to provide the majority of the connecting lines in the fused switch unit, since this, as the major component, will generally be designed to have a longer life than the fuse holders or fuse links, which in some circumstances need to be replaced more frequently.
Flexible connecting lines to the fuse state indicating device for making contact between the bridging element at a fixed end of a spring apparatus which preloads the bridging element are, furthermore, avoided, thus considerably reducing the risk of fuse state indicating device malfunctions caused, in particular, by wear.
The fuse state indicating device preferably has a visual indication, which is advantageously provided within a housing of a fuse holder. The housing of the fuse holder may in this case be a half-housing, which essentially holds only the area of the head contact of a fuse, or may be a full housing, which holds the fuse link essentially completely and leaves free any access points for making contact with the fuse link. The housing of the fuse holder and, possibly, parts of the fused switch unit in this case have a window, so that the visual indication can be seen from the outside.
It is particularly advantageous to provide an optical waveguide, so that light from the visual indication can be passed on at easily visible points. Firstly, this makes it possible for the light which is produced by the visual indication to be passed on independently of the position of the visual indication to easily accessible and easily visible points on the fused switch unit or the fuse holder while, secondly, it is also possible, in addition to or instead of the externally visible visual indication, to pass on the light that it is produced by the visual indication to a light-sensitive sensor, for example a photo cell, in order to allow automatic monitoring and, possibly, control of the fused switch unit.
This is particularly advantageous when a system is formed from a number of fused switch units, so that this allows reliable monitoring, without any delay, of all the fused switch units and, possibly, automatic control of the entire system.